Comparison of Electromagnetic Wave Sensors with Optical and Low-frequency Spectroscopy Methods for Real-time Monitoring of Lead Concentrations in Mine Water

Ilaria Frau,Olga Korostynska,Alex Mason,Patrick Byrne

doi:10.1007/s10230-018-0511-7

Abstract

The feasibility of using novel electromagnetic wave sensors for real-time monitoring of metal pollution in water was assessed. Five solutions with different concentrations of lead (0, 1, 10, 50, 100 mg/L) were measured using several sensing methods: UV–Vis spectroscopy, low frequency capacitance and resistance measurements, and two sensing systems based on microwave technology. With this last approach, two sensing devices were used: a resonant cavity and a planar sensor with gold interdigitated electrode design printed on a PTFE substrate with a protective PCB lacquer coating. Results confirmed the ability of these systems to quantify the lead concentration as changes in spectrum signal at specific frequencies of the electromagnetic spectrum. Spectra were unique, with clearly observed shifts in the resonant frequencies of the sensors when placed in direct contact with different lead solutions, demonstrating the possibility of continuous monitoring with great sensitivity, selectivity, and high spatial and temporal resolution. Consequently, determination of trace and toxic metals using microwave spectroscopy is a promising alternative to traditional grab-sampling and laboratory based analyses. On-line and continuous monitoring of real-time metal concentrations offers the potential for a more effective emergency response and the platform for better scientific understanding and remediation of contaminated mine drainage.

Highlights

Mining can have a significant environmental impact, especially due to the presence of waste materials abandoned in waste heaps (Byrne et al 2012; Hudson-Edwards 2016).Point and diffuse sources determine the dispersion into the environment of toxic inorganic pollutants, mainly metals (Cd, Pb, Cu, Zn, Ni, Fe, etc.), a process driven largely by the oxidation and subsequent hydrolysis of metal sulphides
It is clearly visible that the absorbance is related to the Pb concentration, at the 300 nm peak
High linear correlation with Pb concentration was identified for both parameters: for Cp, where R2 = 0.79 at 30 Hz and

Summary

Introduction

Mining can have a significant environmental impact, especially due to the presence of waste materials abandoned in waste heaps (Byrne et al 2012; Hudson-Edwards 2016).Point and diffuse sources determine the dispersion into the environment of toxic inorganic pollutants, mainly metals (Cd, Pb, Cu, Zn, Ni, Fe, etc.), a process driven largely by the oxidation and subsequent hydrolysis of metal sulphides. Mine waters have a clear correlation between low pH, metal, and sulphate content. This phenomenon, known as acid mine drainage (AMD), has been described as the biggest environmental problem associated with mines (Younger et al 2002). Adequate monitoring and assessment is required to minimise the environmental risk posed by AMD from active and abandoned mining sites all over the world. In the UK, according to the Environment Agency (2008), 9% of the rivers in England and Wales, and 2% in Scotland fail environmental standards because of contaminated drainage from more than 3000 abandoned metal mines. The Mineral Policy Center (Lyon et al 1993) estimated that 557,650 abandoned mines in the USA are polluting over 19,000 km of the nation’s waterways.

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